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Bonded metal components having uniform thermal conductivity characteristics and method of making sameRelated Patent Categories: Stock Material Or Miscellaneous Articles, All Metal Or With Adjacent Metals, Composite; I.e., Plural, Adjacent, Spatially Distinct Metal Components (e.g., Layers, Joint, Etc.), Al-base ComponentBonded metal components having uniform thermal conductivity characteristics and method of making same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20050271894, Bonded metal components having uniform thermal conductivity characteristics and method of making same. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This is a division of co-pending patent application Ser. No. 10/608,898 filed Jun. 27, 2003, which is to issue Aug. 9, 2005, as U.S. Pat. No. 6,926,971, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/392,312 filed Jun. 28, 2002, entitled "Bonded Metal Components Having Uniform Thermal Conductivity Characteristics", and which are incorporated herein in their entirety by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to composite bonded metal cookware, griddle plate or a sole plate for an iron and, more particularly, to bonded composite metal cookware, griddle plate or a sole plate for an iron or the like, having at least one inner metal layer possessing a lower coefficient of thermal conductivity than the other metal layers of the composite so as to cause the heat to saturate in that layer prior to being transferred to the cook or ironing surface. In this manner, hot spots in the cook surface or iron are eliminated so as to improve the performance of the appliance and extend the life of a non-stick surface, if present. [0004] 2. Description of Related Art [0005] It is well known in the art to manufacture multi-layered, composite bonded metal cookware of a variety of metals, most commonly aluminum and/or copper for good heat conductivity along with outer layers of stainless steel for appearance, wear resistance and corrosion resistance. It is also known to employ a layer of a ferro-magnetic material, such as carbon steel or a 400 series ferritic stainless steel in place of the more common 300 series austenitic stainless steel if the cookware is to be used on an induction cooking device. All of these combinations are disclosed in the prior art as taught, for example, in Ulam U.S. Pat. No. 4,646,935; in McCoy et al. U.S. Pat. No. 3,966,426; and Groll U.S. Pat. No. 6,267,830, all of which are incorporated by reference herein. [0006] It is also well-known in the art to coat the cook surface or ironing sole plate surface with a non-stick material such as PTFE ("Teflon.RTM.") or the like. Hot spots may rapidly develop in cookware and sole plates for irons due to the use of conventional metals such as aluminum, copper and stainless steel alone or in composite form. These hot spots not only are troublesome in cooking and ironing but they also cause an accelerated thermal degradation of the non-stick surface. Even if no non-stick surface is present, localized hot spots are undesirable in cookware, since it leads to unequalized cooking. [0007] An attempt to minimize hot spots in cookware is disclosed in U.S. Pat. No. 4,541,411 to Woolf. A multi-ply cookware pan is disclosed by Woolf having inner and outer plies of aluminum or stainless steel enclosing an intermediate ply of a graphite material. The graphite material is not metallurgically bonded to the adjacent metal layers but has thermally anisotropic properties and is oriented so that its thermal conductivity is higher in a plane parallel to the cookware surface than it is in the direction perpendicular to the surface to minimize hot spots on the cooking surface. [0008] Since the graphite layer of Woolf is not metallurgically bonded to the adjacent aluminum and stainless steel layers, and because the aluminum and stainless steel layers are not themselves bonded along the cook surface (due to the intermediate graphite ply), the resultant cookware of Woolf would suffer certain shortcomings. First, due to the non-bonded graphite ply, slight air gaps most probably would be present between the graphite ply and the adjacent layers of aluminum and stainless steel which act as a thermal insulator by way of a barrier or film effect so as to lower the efficiency and uniformity of heat transfer across the interface. In addition, due to the lack of metallurgical bonding between the aluminum and stainless steel layers along the cooking surface of the Woolf cookware, one would expect some thermal warping to occur by virtue of the difference in thermal expansion coefficients of aluminum and stainless steel. [0009] My invention overcomes the problems encountered in the prior art in attempting to eliminate hot spots and achieve more uniform heating across cook surfaces and other applications such as sole plates for ironing (all of which are hereinafter collectively referred to merely as "cookware"). In addition, my invention increases the life of non-stick surfaces by eliminating the hot spot problem of the prior art. Still further, the heat-retardant layer of my invention contributes to the flatness of the cooking vessel during heat-up of multi-layer composites which heretofore might be present due to differences in thermal expansion coefficients of the several layers of different metals in the composite SUMMARY OF THE INVENTION [0010] Briefly stated, my invention provides composite, bonded metal cookware having outer layers of aluminum and/or stainless steel with a core construction comprising a layer of a heat-retardant metal such as titanium, titanium alloy, stainless steel or the like, bonded on both sides to one of a layer of pure aluminum or a layer of Alclad aluminum. My invention also includes the method of making said bonded components. In one presently preferred construction, a titanium Ti 46 alloy strip having a thickness of about 0.030-0.035 inch is bonded on both surfaces to strips of Alclad aluminum each having a thickness of about 0.035-0.040 inch, with a layer of 304 stainless steel 0.015-0.017 inch bonded to each of the outer surfaces of the Alclad aluminum. Prior to roll bonding, the surfaces of the strips of the above materials are mechanically abraded by wire brush, wheel or the like to clean the surfaces and expose bare, unoxidized metal. The sheets are stacked in the following order: stainless steel layer--Alclad layer--titanium layer (or stainless steel layer)--Alclad layer--stainless steel layer; the stack may then be heated or soaked to a temperature of 550.degree. F.-600.degree. F. in an oxygen-containing atmosphere (regular atmosphere), or at a higher temperature in an O.sub.2-free atmosphere furnace. A temperature below about 550.degree. F. fails to provide a Ti bond during rolling, while a temperature above about 600.degree. F. causes the formation of Ti oxides in an oxygen-containing furnace atmosphere. Such oxides prevent sound metallurgical bonding. [0011] The so-heated, ordered stack of sheets is then hot rolled in a first pass in a rolling mill while at 550.degree. F.-600.degree. F. in the oxygen-containing atmosphere at a reduction of at least 5% up to 10% to achieve a bond between the Ti and Al, and between the Al and the outer stainless steel layers. The bonded pack can then be reheated if necessary and rolled in a second pass at a 10-20% reduction. The finished composite is then preferably heat treated at 650.degree. F.-700.degree. F. to improve the bonding strength by way of diffusion bonding between adjacent layers. [0012] The material so processed can then be blanked and formed by way of drawing in a conventional manner into the desired cookware shapes. [0013] Comparative thermographic imaging of the composite material of the present invention indicates a uniformity of heating across the inner cook surface which is free of hot spots. [0014] If induction cookware is desired, a layer of ferro-magnetic material, such as carbon steel of a 400 series ferritic stainless steel, can be applied to the outer (lower) surface of the cookware, i.e., that surface which is closest to the inductor. In addition, a non-stick surface can be applied to the cook surface or iron sole plate surface on the stainless steel layer or, alternatively, along an aluminum layer, if desired. BRIEF DESCRIPTION OF THE DRAWINGS [0015] FIG. 1 is a cross-sectional view of one presently preferred embodiment of a bonded metal composite according to the invention; and [0016] FIGS. 2-3 are cross-sectional views of other presently preferred embodiments of the invention similar to FIG. 1. DETAILED DESCRIPTION OF THE INVENTION [0017] With reference now to the appended drawings, FIG. 1 schematically depicts, in cross section, one preferred embodiment of a bonded metal composite sheet 2 of the present invention. The composite sheet 2 is a multi-layered, rolled bonded construction comprising a layer 4 of a material having a lower coefficient of thermal conductivity than the other metal layers in the composite sheet 2. The presently preferred material for the lower thermal conductivity layer 4 is titanium or titanium alloy because of its relatively lower heat conductivity coefficient compared with the aluminum coupled with its light weight, which is comparable to aluminum. Stainless steel has a coefficient of heat conductivity similar to that of titanium and may be used for the layer 4. Stainless steel is less expensive than titanium but is heavier, adding to the weight of the cooking vessel. In the composite sheet 2 of FIG. 1, the titanium layer 4 is roll bonded on both sides between aluminum layers 6 and 6'. The aluminum layers 6 and 6' comprise pure aluminum of the 1100 series or the layers 6 and 6' may be Alclad aluminum sheet. Alclad aluminum is made from an aluminum alloy core, such as 3003 alloy, roll bonded to outer layers of pure aluminum. The 3003 aluminum alloy core provides improved strength while the outer layers of pure aluminum provide good roll bonding properties. For improved roll bonding, the titanium layer (or stainless steel) 4 should be bonded to a layer of pure aluminum. It will be understood that when reference is made hereinafter to the titanium layer, that stainless steel could be substituted therefor, as well. The aluminum layers 6, 6' in the embodiment of FIG. 1 are, in turn, roll bonded to layers 7 and 8 of stainless steel. [0018] The stainless steel layer 8 defines the inner cook surface of the composite sheet 2 of FIG. 1 and is preferably made from an austenitic stainless steel such as type 304 stainless steel which offers good corrosion resistance and deep drawing properties. The outer stainless steel layer 7 is directly adjacent to the heat source and may also be made from an austenitic grade of stainless steel such as 304 or from aluminum (brushed, polished or anodized). If the cookware is to be used for induction type cooking, then the outer layer 7 is made from a ferromagnetic material, such as carbon steel or from a ferritic stainless steel, or from a composite containing a ferritic stainless steel or carbon steel. A presently preferred ferritic stainless steel for use in layer 8 is selected from the 400 series of stainless steels such as type 409 stainless steel. A roll bonded composite comprising a layer of a 400 series ferritic stainless steel sandwiched between layers of 300 series austenitic stainless steel may also be used for layer 8 when the cooking vessel is intended for use with an induction cooking range. Of course, such induction cookware can also be used with conventional gas or electric ranges. [0019] Additional presently preferred embodiments of my invention are depicted in FIGS. 2 and 3 wherein the roll bonded composite sheets of my invention are identified by reference numerals 20 and 200, respectively. In the one presently preferred embodiment of FIG. 2, the roll bonded composite sheet 20 comprises a layer of titanium or titanium alloy 40 roll bonded to layers 60 and 60' of aluminum or Alclad aluminum which, in turn, are roll bonded to layers of stainless steel 70 and 80. The lower layer 70 may be one of austenitic or ferritic stainless steel or a composite, i.e., a layer 70 of ferritic stainless steel with a further outer layer of austenitic stainless steel (not shown) roll bonded thereto, all as described above with reference to FIG. 1 and composite sheet 2. Continue reading about Bonded metal components having uniform thermal conductivity characteristics and method of making same... Full patent description for Bonded metal components having uniform thermal conductivity characteristics and method of making same Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Bonded metal components having uniform thermal conductivity characteristics and method of making same patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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